How to Choose a Power Supply for LED Strips and Modules: Power Calculation
The short answer: add up the power of everything you connect, add a 20% reserve and take the next standard power supply above that figure. The voltage must match the LEDs exactly — 12V for 12V products, 24V for 24V ones. Below is the calculation step by step, a table of ready examples and the difference between indoor and waterproof units.
The formula
Power supply (W) = total LED power (W) × 1.2
- Find the total power. For strips and neon: length in metres × watts per metre. For modules: number of modules × watts per module. Both figures are in the product name.
- Add a 20% reserve. A power supply that runs at its limit heats up and ages faster. With a reserve it works cooler and lasts longer.
- Round up to the next standard size. Power supplies come in fixed steps: 35, 60, 100, 150, 200 W and so on. Never round down.
Ready examples
| What you connect | Calculation | With 20% reserve | Power supply |
|---|---|---|---|
| COB 11 W/m × 5 m | 11 × 5 = 55 W | 66 W | 75 W (IP20) / 100 W (IP67) |
| S-type 60 7.2 W/m × 10 m | 7.2 × 10 = 72 W | 86.4 W | 100 W |
| SWP 120 12 W/m × 5 m | 12 × 5 = 60 W | 72 W | 75 W (IP20) / 100 W (IP67) |
| RGB 14.4 W/m × 5 m | 14.4 × 5 = 72 W | 86.4 W | 100 W |
| NeonFlex 6x12 9.6 W/m × 10 m | 9.6 × 10 = 96 W | 115.2 W | 150 W |
| Shine 4 1.46 W × 50 | 1.46 × 50 = 73 W | 87.6 W | 100 W |
| OPTX 3 0.72 W × 100 | 0.72 × 100 = 72 W | 86.4 W | 100 W |
| Mini 2 0.3 W × 200 | 0.3 × 200 = 60 W | 72 W | 75 W (IP20) / 100 W (IP67) |
For outdoor signs the same calculation applies; only the type of the unit changes — see below.
Indoor or waterproof
Indoors and inside dry light boxes use open-frame units in a perforated metal case, such as Mean Well LRS (35–350 W). They cool well, but are not protected against moisture.
Outdoors and in damp places use sealed IP67 units: Scharfer SCH (18–400 W) or Mean Well LPV and XLG. They work in rain, snow and dust.
12V or 24V
The power supply must have the same voltage as the LEDs: a 12V strip on a 24V supply burns out at once, a 24V strip on 12V barely lights. For long runs 24V products are easier — the voltage drop along the strip is smaller.
Common mistakes
- Taking a power supply with no reserve — it overheats and fails early.
- Putting an indoor unit into an outdoor sign.
- Feeding a long strip from one end only: the far end is dimmer. Feed it from both ends or every 5 metres.
- Mixing 12V and 24V products on one power supply.
Questions and answers
Can I take a more powerful power supply than calculated?
Yes. The LEDs draw only what they need; a bigger unit simply works with a larger reserve.
Can several strips share one power supply?
Yes, connected in parallel. Add up their power and apply the same formula.
Does the power supply dim the light?
No. For dimming or colour change you need a dimmer or a controller between the power supply and the LEDs.
All units are in the power supplies section. Not sure which one to take? Write to us in the chat — tell us the product and the length or quantity, and we will pick the unit.
